This invention relates to oceanic instrumentation systems, particularly expendable systems, where a wire cable is utilized to suspend an immersible package at some predetermined depth from a buoy and an insulated conductor usually inside the suspension cable is used to transmit signals between the immersible package and the buoy. The buoy usually contains radio equipment for communication with air or surface craft.
A sonobuoy is a typical expendable system which may employ the present invention to great advantage. It was developed as a submarine detector to be dropped from aircraft, but the preesnt invention is not limited to submarine detection applications. It is applicable to any instrumentation system for commerical or scientific applications. Consequently, although the present invention will be described in a specific embodiment with reference to a sonobuoy, it is not intended that the claims be limited to a sonobuoy.
An air-dropped sonobuoy assembly is comprised of a buoy and a battery-equipped instrumentation package. Attached directly to the instrumentation package is a cable pack which pays out cable as the instrumentation package and cable pack descend until the desired depth is reached. That depth is variable over a wide range and may be determined by a clock in the instrumentation package (which begins operation when the batteries are activated upon being immersed in seawater) from a known rate of descent. Alternatively, a pressure transducer in the instrumentation package may sense the desired depth pressure and stop the cable pack from paying out additional cable.
The cable which suspends the instrumentation package and cable pack is normally comprised of the insulated conductor through which the instrumentation package transmits data to the receiver/transmitter in the buoy. The insulated conductor is contained in a close-fitting jacket or casing of braided, high tensile strength synthetic aramid fiber. This outer braided material for the insulated conductor provides the necessary tensile strength required by the cable for the weight of the instrument package and cable pack in the water.
The cable in the pack is usually in excess of 16,000 feet in order for the same sonobuoy assembly to be used over a wide range of ocean depths. Consequently, there is usually a significant length of cable left coiled in the pack. This practice of providing excess cable for a particular mission presents two significant problems. The first problem is to provide a means for terminating the process of paying out cable. The second problem is to provide a means for shunting the coiled cable remaining in the pack. A solution to this second problem is significant because transmission through coiled cable remaining in the pack, plus the payed out length of cable, may require an extremely elaborate and expensive electronic transmitter and receiver to compensate for the poor frequency response and distortion of the coiled cable in the pack. Experience has demonstrated that transmission through the coiled cable in the pack is too complex and costly to develop, particularly when one must consider the large range of coiled cable that may remain in the pack. It is preferable to simply bypass the coiled cable in the pack, but that presents yet another problem of mechanically penetrating the cable insulation to achieve an electrical connection while maintaining a pressure seal around the connection thus made. The significance of this problem can be appreciated when it is recognized that the slightest leakage current from the electrical connection to the seawater will quickly erode the electrical connection by electrolysis.